Process for separating the constituents of air



Oct. -1, 1946.

1 c. c. VAN NUYS PROCESS FOR SEPARATING THE CONSTITUENTS OF AIR Filed Dec. 17, 1943 h wowhukkkb R x. Q m w km -H- 9 w M w $3; 1 Q V H.308 &m, w 6 w 4 M w R% v\\ m v 5 ES Q .I w Q w we .3 Lil ATTORNEY;

This. invention relates t 'tively high pressure of the --pheres.

-ciency ofv the "cycle and complicated equipment.

Patented Oct. 1, 1946 1 e PRooEssFoa SEPARA'IING THE UENTS OFAIRf Claude Van Nuys, Greenwich, Conn, assignor to Air ReductionCompany,

Incorporated, New

York, N. 'Y., a corporation of New York Application December 1'7,

the separation of atmosphericair'into its constituents by liquefaction and rectification, and particularly to improvements'in the method and apparatus therefor.

In commercial liquefaction methods of separating oxygen fromthe atmosphere as heretofore practised, the necessary refrigeration to attain .low; temperatures is obtained'by compression and subsequent expansion of the-air treated. This necessitates initial compression of the air to rela- Such compression can be attained only in reciprocating compressors which require oil lubrication. The oxygen of the air under such pressures and at the temperatures resulting from compression causes decomposition of; the lubricating oil and the introduction-to the, air stream of; substantial proportions of hydrocarbons in addition to any which may be Since the hydrocarbons are I not removed, from the air stream by the usual treatment intended to separate moisture and carbon dioxide, they tend to accumulate and eventually ,find. their way .to the compartment of the apparatus where liquidoxygen accumulates. The presence of such material in contact with pure oxygen, whether liquid or gaseous, is undesirable. 'Hence very elaborate attempts have been made heretofore to eliminatethe hydrocarbons at some-point intermediate compression of the air andthe' formation of liquid or vapor rich in oxygen in which the hydrocarbons might accumulate. Such attempts.

involve operations which interfere with the 'effithe use of necessarily Furthermore, these attempts have failed substantially to achieve the desired object." It is still possible for hydrocarbons derivedfrom theiubricating oilito accumulate at points'in-the apparatus where'gases or liquids rich in oxygen are present. I w

' t is' the object of the present invention to provide a simple "and effective oil in the compressulting from decomposition of sion of the air can'be eliminated and further iniprovementsinthe separation of oxygen fromjthe atmosphere can be obtained othe b t and ad a a es of the nrcnflo willbe apparent as it is betterunderstoodb rei- "erenceto the following specificationfand the ac- 'com'panying drawingtwhich;illustrates diagram- 1 order of 15-20 atmos-.

present; The-use of vspeciallubricating oils does not avoid this source of contamination.

e q cad nc ratus'wh'ereby the "presenceof' hydrocarbon re- I "f th s-i .of the invention.

of the invention. tainable in various atmosphere and tained in the air separation reference 'to' the drawing, in rectification, column I bubble caps 1.

.with an outlet 8 throughwhich .therefrom through the trays 1943, Serial No. 514,593 slolaiins. (01. 62-1755) matically an apparatus suitable for the practice In accordance" with the present invention, the air tobe separatedis not utilizedto produce any refrigeration in the cycle. I employ instead a separate-mitrogen cycle which acts as a heat transfer agent everywhere in the cyclerThe air need be compressed in accordance with my inventiononly to pressuresnot substantially higher than three atmospheres absolute. Usually a pressure of two atmospheres, or sufficient pressure only to ensure movement of the gas through the apparatus is needed to accomplish the purpose Such pressures are easily attypes of blowers which require no internal lubrication. Hence no lubricating oil and decomposition products inafter described effectively increases the proportion of'oxygen which can be recovered from the thepurity of the product,

Thenitrogen which affords the refrigerative .efiect is compressed, circulated and expanded in such a way as to providestrfficient cold so that theair can be liquefied at -lowpressure. The

nitrogen of the refrigeration cycledoes not mingle .at ;any point with the air undergoing separation. Hence the presence of hydrocarbons in the nitrogencycle is not inimical to the method and afiords no possibility of accumulation of hydrocarbons inthe presence of oxygen or products rich in oxygen. The nitrogen can be compressed lto the necessary pressure for example ,2500 pounds per square inch. in starting the apparatus, and from-900 170 1,009 pounds per squareinch thereafter,- in any available form of compressor. .OiLlubrication maybe used. nitrogen necessary for .de end'upon th e The quantity of r provide this liquid; a p evio sl e mi sed t Lethe; i it al pres u p e e y j npt greater than threeatmospheresfabsolute in any thereof are mingled with the air which is eventuallyseparated to recover oxyen therefrom. The-procedure as herethe refrigeration-cycle will which 5' indicate a changer l9 and bya valve 35 to'purge the column suitable apparatus such as a blower (not shown) is introduced through a pipe 9 into an exchanger I and travels about pipes H and I2 therein in heat exchange relation with cold products of the separation. The air thus cooled is delivered through a pipe l3 to the bottom of a backward return condenser. l4 having tubes l5 and bafileslB therein. The air flows upwardly through "the tubes, being subjected therein to backward return condensation by heat exchange with nitrogen liquid and vapors supplie'dthrough a pipe 1:1.

The liquid from the condenser I4, which is enriched in oxygen, is delivered by a pipe I8 controlled by a valve l9 to an intermediate level of the column '5.

The gaseous residue from the tubes l5 consisting principally of nitrogen i'sedelivered by apipe 2!! to a condenser 2| containing tubes 22 through which the residue flows in heat exchange relation with liquid nitrogen supplied through a pipe 23. The surplus liquid from the condenser 2! overflows through the pipe IT. The residue is condensedby heat exchange with the liquid nitrogen and "is del'ivered'by a pipe 24 controlled by a valve 25 to the topof the column 5 and affords the reflux nitrogen liquid required to effectively separate substantially all of theaoxygen from the air treated:

efiluent nitrogen from the column is delivered by the pipe 8 to'the tubes H of the exis withdrawn through a pipe 26 to any suitable receptacle or to the atmosphere. 'lfh'e oxygen product may be withdrawn as a liq- 'uid th-rcugh a pipe 2? controlled by a valve 28 and delivered by a liquid pump 29 to a pipe 33 which delivers it to the pipes i 2 of the exchanger l0 wherein the liquid is vaporized. The oxygen product is withdrawn through a pipe 3| and delivered to any suitable storage receptacle. Al-

ternat'ively, oxygen in the form of vapor may be withdrawn through a pipe 32 controlled by a valve 33 and. delivered to the pipe 3%. Liquid oxygen maybe withdrawn through a pipe 34 controlled of any impurities which-may accumulate therein. To afford-the necessary refrigeration for the system, nitrogen is compressed in a compressor 36 to a suitable pressure as hereinbefore described and delivered by a pipe 31 to a cooler 38'. 39 to an exchanger All and travels about tubes 41 "therein where it is further cooled by heat exchange with cold nitrogen vapor returning in the cycle. The cold nitrogen is delivered by a pipe 42-to a coil dt which is immersed in the liquid oxygen accumulating in the bottom of the col- The resulting heat exchange cools the nitrogen and causes vaporization of a portion of the liquidto maintain the vapor which rises through-the column. The sub-cooled nitrogen is then delivered through a pipe 44 to the tubes 45 of an exchanger 5'5 where it is liquefied by heatexchange with cold nitrogen vapors enterin'g'the liquefier through a pipe 41. These vapors escape 'throgh a, pipe 48 to the exchanger 46 and aft-"er passing through the tubes M of the exchanger, are delivered by a pipe 49 to the compressor 3'6.

Ihegliquid nitrogen from the liquefier '46 is delivered through a pipe 50 and throttle valve. 5| to the pipe 23 and thus to the condenser 2|, af-

fording the liquid nitrogen necessary to liquefy thenitrogen reflux for the column .5 and also to elrect theinitial backward. return condensation of the air entering the system. The nitrogen Thence the nitrogen is delivered by a pipe liquefaction the air through the the compressed air to two fractions enrichedrespectively in oxygenand nitrogen .by indirect heat..,excha-nge with the liqpoint mingle With the air undergoing separation or the products thereof. Nitrogen separated from the air is withdrawn, as is also the oxygen product, independently of the refrigeration cycle. Since the nitrogen employed for refrigeration travelsxin an independent cycle, it is immaterial whether or not it may carry hydrocarbons. These hydrocarbons, if present, cannot mingle with the air undergoing separation and thus arrive at a point in thesystem where oxygen or products rich in oxygen are present. Thus the liquid oxygen which-accumulates in the bottom of the column 5 is free from any contaminating hydrocarbons which might have been introduced owing to the necessity of employing'oil in the initial compression of the air. The use of the bloiver'to compress the air obviates that possibility.

The invention as described affords a practical and simple solution of a problem which has existed for many years in the commercial production of oxygen by liquefaction and rectification. It also permits substantially total recovery of the oxygen content of the air, since the nitrogen reflux which issupplied at the top of the column prevents the escapeof oxygen in'the efiiuent.

Various changes may be made in the details of procedure and in the apparatus as described without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of separating the constituents of" atmosphere air in a liquefaction apparatus by liquefaction and rectification which comprises compressing n'itrogen toa relatively high pressure, liquefying the nitrogen, compressing the air to a pressure not materially in excess of that required to overcome the resistance to travel of the air through the apparatus without abrupt change in pressure, subjecting the air to indirect heat exchange with the liquid nitrogen to separate liqu id fractions enriched respectively in oxygen,

and nitrogen, and rectifying the two fractions to recover substantially pure liquid oxygen.

2; The method of separating the constituents of: atmospheric air'in a liquefaction apparatus 'by and rectification which comprises compressing nitrogen to a relatively high pressure, liquefying the. nitrogen, compressing the air :to;a pressure notmateria'lly'in excess of that required to overcome the resistance to travel of apparatus without abrupt change; in pressure, subjecting the air to backward- .return condensation "with partial condensation-thereof, condensing the gaseousresidue from the backward'returnflcondensation by indirect heat exchange'wit'h, the liquid nitrogen to separate liquid fractionsenriched respectively in oxygen and nitrogen, and rectifying. the two fractions to recover substantially pure liquid oxygen 3. The methodof separating the constituents of atmospheric .air by liquefaction. and rectification. whichcomprises compressing the air toa relatively low pressure such that expansion from thatpressure will not produce refrigeration suffrcient to effect liquefaction; thereof, subjecting coolingand liquefaction in uid'nitrogen,rectifyingthe two fractions to recover substantially pure-liquid oxygen andmaintaining the refrigeration necessary for the operation by compressing nitrogen to relatively high pressure and liquefying the nitrogen to supply continuously the liquid required to effect liquefaction of the air.

4. The method of separating the constituents of atmospheric air by liquefaction and rectification which comprises compressing the air to a relatively low pressure suoch that expansion from that pressure will not produce refrigeration sufficient to effect liquefaction thereof, subjecting the compressed air to cooling and liquefaction in two fractions enriched respectively in oxygen and nitrogen by indirect heat exchange with the liquid nitrogen, rectifying the two fractions to recover substantially pure liquid oxygen and maintaining the refrigeration necessary for the operation by compressing nitrogen to relatively high pressure and liquefying the nitrogen by heat exchange successively with the liquid oxygen and cold nitrogen vapors to supply continuously the liquid required to effect liquefaction of the air.

5. The method of separating the constituents of atmospheric air which comprises compressing the air to a relatively low pressure without contamifiating the air with lubricating oil, maintaining a separate nitrogen cycle including compression of the nitrogen to a relatively high pressure and liquefaction of the nitrogen, subto indirect heat exchange with the liquid nitrogen to separate two liquid fractions respectively enriched in oxygen and nitrogen, and rectifying the two fractions to recover 6. The method of separating the constituents of atmospheric air which comprises compressing the air to a relatively low pressure without contaminating the air with lubricating oil, mainsubstantially pure liquid oxygen.

of atmospheric air 6 taining a separate nitrogen cycle including compression of the nitrogen to a relatively high pressure and liquefaction of the nitrogen by heat exchange with cold nitrogen vapors, subjecting the air at low pressure to indirect heat exchange with the liquid nitrogen to separate two liquid fractions respectively enriched in oxygen and nitrogen and rectifying'the two fractions to recover substantially pure liquid oxygen.

7. The method of separating the constituents of atmospheric air which comprises compressing nitrogen to a relatively high pressure sufficient to afford the necessary refrigeration to liquefy the nitrogen, liquefying the compressed nitrogen, compressing the air to a relatively low pressure, vaporizing the liquid nitrogen by backward return condensation of the air with partial condensation thereof, liquefying the gaseous residue from such backward return condensation to provide two liquid fractions enriched respectively in oxygen and nitrogen, and rectifying the two fractions to recover substantially pure liquid oxygen. 8. The method of separating the constituents which comprises compressing nitrogen to a relatively high pressure sufficient to afford the necessary refrigeration to liquefy the nitrogen, liquefying the compressed nitrogen, compressing the air to a relatively low pressure, vaporizing the liquid nitrogen by backward return condensation of the air with partial condensation thereof, liquefying the gaseous residue from such backward return condensation to provide two liquid fractions enriched respectively in oxygen and nitrogen, rectifying the two fractions to recover substantially pure liquid oxygen, and recompressing the vapor produced by vaporizing the liquid nitrogen to maintain the cycle.

CLAUDE C. VAN NUYS. 

